1. Field of the Invention
The present invention relates to a surround circuit using an A/D conversion circuit, a delay circuit and a D/A conversion circuit.
2. Description of the Related Art
A conventional audio reproducing apparatus is provided with a mode for reproducing the sound of music as heard wihin a concert hall, a stadium, a church or other surrounding sound fields. By operating the audio apparatus, a listener can obtain a desired surround mode. Such surrounding is for the most part produced by delaying audio signal components for a predetermined time to produce a simulated reflected sound by superimposing an audio reproduced sound and the simulated reflected sound. FIG. 1 shows a conventional surround circuit for producing a surround sound.
In FIG. 1, an audio signal is applied via an input terminal IN to an A/D conversion circuit 1, where it is converted to a digital signal by a sampling signal of a fixed frequency. The digital signal is delayed in a delay circuit 2, which delays components of the digital signal by different delay times. Therefore, the delay circuit 2 generates an output signal al delayed by a first delay time, an output signal a2 delayed by a second delay time longer than the first delay time, an output signal a3 delayed by a third delay time longer than the second delay time, and an output signal a4 delayed by a fourth delay time longer than the third delay time.
The output signals a1 to a4 of the delay circuit 2 are converted to analog signals on a fixed sampling frequency in respective first to fourth D/A conversion circuits 4 to 7. Output signals of the first to fourth D/A conversion circuits 4 to 7 are added in an addition circuit 8. An output signal of the addition circuit 8 and the audio signal from the input terminal IN are added in an addition circuit 10. Therefore, an output signal of the addition circuit 10 is constituted by superimposing onto the audio signal signals for reproducing various simulated reflected sounds onto the audio signal.
However, in the circuit of FIG. 1, to produce various simulated reflected sounds, the delay circuit 2 generates a number of output signals with different delay times. There is causes a problem that a number of D/A conversion circuits corresponding to the output signals of the delay circuits 2 must be used, which may be a large number. Therefore, such circuits are disadvantageously complicated and their size is enlarged.